Results from mass testing in the Italian town, Vo', show that antibodies from a COVID-19 infection might last for at least nine months after infection. And it appears that symptomatic and asymptomatic people have similar levels of antibodies.
The team tested 2,602 people out of a population of just over 3,300 to understand infection rates, spreading, and the development of antibodies from COVID-19. The work, published in Nature Communications, required multiple assessments of infections. The people were tested in February/March, then again in May, and finally in November.
Three tests were used to assess the level of antibodies. By May, 3.5 percent of the population had been infected based on the tests, although some of them had no symptoms. The team found that 98.8 percent of people infected (whether asymptomatic or not) had detectable levels of antibodies in November.
The antibodies were less abundant in November suggesting that the protection fades. The research also found that some people had an increase in antibodies between May and November. This might indicate the possibility of reinfection leading to an increased reaction from the immune system.
"We found no evidence that antibody levels between symptomatic and asymptomatic infections differ significantly, suggesting that the strength of the immune response does not depend on the symptoms and the severity of the infection," lead author Dr Ilaria Dorigatti from Imperial College London, said in a statement.
"However, our study does shows that antibody levels vary, sometimes markedly, depending on the test used. This means that caution is needed when comparing estimates of infection levels in a population obtained in different parts of the world with different tests and at different times."
The scientists also looked at how SARS-CoV-2, the virus that causes COVID-19 spread in the town. They were particularly interested in household transmission and discovered that there was a one in four chance of passing the virus to a relative.
Even more interestingly, it appeared that once again the vast majority of the virus spread (79 percent) was done by a minority of the people. One in five infections were responsible for it. Most infected people did not pass it on, but the rest help to it spread it. And this is why behavioral factors are key. Limiting the number of contacts, physical distancing, and continuing to wear masks significantly reduces the risk of transmission.
"It is clear that the epidemic is not over, neither in Italy nor abroad. Moving forward, I think that it is of fundamental importance to continue administering first and second vaccine doses as well as to strengthen surveillance including contact tracing. Encouraging caution and limiting the risk of acquiring SARS-CoV-2 will continue to be essential," Dr Dorigatti added.